India, the second-most populous country in the world, will soon experience rapid aging of its population. By 2050, India's older population (> 60 years old) is projected to reach 320 million (about the current size of the entire US population), representing an increase from 8 to 20 percent of its total population. The growing number of older people will drive a large increase in the prevalence of dementia in India, far exceeding the capacity of the private care system that currently predominates for the elderly. The Longitudinal Aging Study in India (LASI), a survey of 50,000 Indians representative of the older population across the nation and within its states and union territories, provides a unique opportunity to examine this and related issues. LASI is the most ambitious nationally representative study of the physical, mental, economic, and social well-being of the country's older population. Harmonized with other Health and Retirement Study (HRS) surveys, it offers an evidence base that can be used to compare the effects of social policies aimed at supporting older persons in India with policies used in other countries around the world. The objective of the proposed research is to supplement the current LASI in order to estimate the prevalence of dementia and mild cognitive impairment (MCI) in India. Previous efforts to identify dementia in developing nations have typically relied on non- representative samples in geographically restricted regions. In this application, we aim to develop a protocol for the assessment of dementia and MCI to be used within community settings in the ongoing, nationally representative LASI. To do so, we will first conduct in-depth cognitive testing for a sub-sample of LASI respondents at regional geriatric hospitals in India. Specifically, we will administer two leading dementia assessment protocols - the HRS Harmonized Cognitive Assessment Protocol (HCAP) and the 10/66 Dementia Protocol - to approximately 2,000 respondents at least 60 years of age and stratified by their Wave 1 cognition test results, as well as their proximity to collaborating regional geriatic hospitals where the assessments will occur. Based on prognostic evaluation of the protocols, we will develop a short (15-minute) dementia assessment module and administer it in Wave 2 to persons with a high probability of having dementia and MCI as well as to the 2,000 persons participating in the earlier assessment. Using these data, we will estimate prevalence rates of dementia and MCI in India for the population and sub-populations. We will provide to the research community data generated from the in-depth cognitive testing at regional geriatric hospitals and from the administration of the short dementia assessment module during Wave 2, both linked to the on-going LASI main survey. Our harmonized protocol for dementia and MCI assessment will enable researchers to make comparisons with prior findings in India using the 10/66 protocol as well as to conduct cross-country studies with the United States, England, China, and other countries that implement the HRS HCAP protocol.